ABCs of z/OS System Programming Volume 3 - IBM Redbooks

In addition to the 3494 VTS components B10, B18, and B20, the Peer-to-Peer VTS consists
of the following components:
► The 3494 virtual tape controller model VTC
The VTC in the Virtual Tape Frame 3494 Model CX1 provides interconnection between
two VTSs with the Peer-to-Peer Copy features, and provides two host attachments for the
PtP VTS. There must be four (for the Model B10 or B18) or eight (for the Model B20 or
B18) VTCs in a PtP VTS configuration. Each VTC is an independently operating,
distributed node within the PtP VTS, which continues to operate during scheduled or
unscheduled service of another VTC.
► The 3494 auxiliary tape frame model CX1
The Model CX1 provides the housing and power for two or four 3494 virtual tape
controllers. Each Model CX1 can be configured with two or four Model VTCs. There are
two power control compartments, each with its own power cord, to allow connection to two
power sources.
Peer-to-Peer copy features
Special features installed on 3494 Models B10, B18, and B20 in a Peer-to-Peer configuration
provide automatic copies of virtual volumes. These features can be installed on existing VTS
systems to upgrade them to a Peer-to-Peer VTS.
VTS advanced functions
As with a stand-alone VTS, the Peer-to-Peer VTS has the option to install additional features
and enhancements to existing features. These new features are:
► Outboard policy management: Outboard policy management enables the storage
administrator to manage SMS data classes, storage classes, management classes, and
storage groups at the library manager or the 3494 specialist.
► Physical volume pooling: With outboard policy management enabled, you are able to
assign logical volumes to selected storage groups. Storage groups point to primary
storage pools. These pool assignments are stored in the library manager database. When
a logical volume is copied to tape, it is written to a stacked volume that is assigned to a
storage pool as defined by the storage group constructs at the library manager.
► Tape volume dual copy: With advanced policy management, storage administrators have
the facility to selectively create dual copies of logical volumes within a VTS. This function
is also available in the Peer-to-Peer environment. At the site or location where the second
distributed library is located, logical volumes can also be duplexed, in which case you can
have two or four copies of your data.
► Peer-to-Peer copy control
There are two types of copy operations:
– Immediate, which creates a copy of the logical volume in the companion connected
virtual tape server prior to completion of a rewind/unload command. This mode
provides the highest level of data protection.
– Deferred, which creates a copy of the logical volume in the companion connected
virtual tape server as activity permits after receiving a rewind/unload command. This
mode provides protection that is superior to most currently available backup schemes.
► Tape volume cache management: Prior to the introduction of these features, there was no
way to influence cache residency. As a result, all data written to the TVC was pre-migrated
using a first-in, first-out (FIFO) method. With the introduction of this function, you now have
the ability to influence the time that virtual volumes reside in the TVC.
500 ABCs of z/OS System Programming Volume 3